The present invention relates to surfboards, and more particularly to surfboards with a lateral foil system.
Surfboards are watercraft that can be ridden on water, typically in waves. The term “surfboard” may include, without limitation, body boards, wind surfing boards, body surfing suits, stand up paddle boards, wake surfing board and other hulled craft which carry a rider, and usually utilizing the energy of water waves. Surfboards typically rely on hydrostatic lift, or buoyancy, to eventually achieve a state of planing, in which forward movement of the surfboard is supported by hydrodynamic lift (planing hull lift) of water moving along the surfboard's bottom surface.
With forward motion, surfboards generate lift that buoy both the craft and rider while being propelled along a wave face in the planing hull lift mode. Planing hull lift of surfboards is supported by bottom channels and concavities, but can also be powered by control surfaces, such as fins, that provide foil lift. FIG. 28 illustrates examples of planing hull lift versus foil lift. Conventional fins extend downwardly from the bottom surface of the surfboard, as shown in FIG. 28.
For nomenclature that is pertinent to the background of the disclosure herein, and as illustrated in FIG. 29, a “nose” is the front area of surfboard and a “tail” is the rear area of surfboard. A “deck” is the top surface of the surfboard, and a “bottom” is the under or bottom surface of the surfboard. A “length overall” (LOA) is the distance from the tip of the tail to the tip of the nose, and a “width” is the widest distance in plan view. The “center line” is the line bisecting the width. A “rail” is the area of surfboard where the deck transitions to the bottom, and a “rail apex” is the most outboard point of the rail.
FIG. 30 shows a reference coordinate system, in which an X-Axis runs along the surfboard longitudinal axis and is positive forwards with the origin at the rear most point of surfboard. A Y-Axis is transversal and positive to port with the origin on the surfboard centerline. A Z-Axis is vertical and positive upwards with the origin level with the lowest point along the centerline. With respect to a local reference system, at any transverse cross section a reference axis runs through the rail apexes from which an anhedral angle is measured (negative downward). At any location along the rails, an angle of attack is measured (positive upward) from the tangent of the curve running through the rail apexes.
Present surfboard designs rely heavily on the surfboard's rails and bottom shape to provide lift in the form of planing hull lift. However, lift generated from a foil, i.e. foil lift, is of an order of multiple times more efficient than planing surface lift. Also, various fin setups with generally vertical orientations have been developed to provide hold (and propulsion) on a wave face. However, when viewed against actual wave particle motions in the regions of a wave being surfed, the fins are far from optimal orientation relative to the surfboard itself.